Electrohydraulic solenoid



June 20, 1944.

H. o. PUTT 2,352,119

ELECTRO-HYDRAULIC SOLENOID Filed Sept. 17, 1942 2 Sheets-Sheet l mu I: 24

June 20, 1944. H. o. PUTT 2,352,119

ELECTED-HYDRAULIC SOLENOID F iled Sept. 17, 1942 2 Sheets-Sheet 2 Patented June 20, 1944 UNITED STATES PATENT OFFICE- .ELECTROHYDRAULIO SOLENOID HarlieO. Putt, Elkhart, Ind.

- Application September 17, 1942, SerialNo. 458,707

2 Claims (o1.175-,-s'z2) It" is the object of my invention to provide a novel electro-hydraulic solenoid for the controlled operation of carburetor throttle valves, where a predetermined rate of movement or a slightly delayed action is essential.

It is well known that the magnetic pull on the plunger of an ordinary solenoid increases rapidly as'the plunger enters the coil. This pull varies directly with plunger mass within the coil and inversely as the square of the air gap and current input, assuming that the plunger is of uniform diameter.

With any-given field intensity (sufficient to start movement of the plunger) and an ordinary solenoid in a vertical position, the plunger would bedrawn into the solenoid at a rapidly accelerated rate or velocity, until its mass was equally disposed'therein, which position it would maintain even thoughthe field intensity were reduced approximately four times.

It will be evident therefore, that a simple solenoid and plunger could not be employed to provide a uniform acceleration or pull directly proportional to energy input for the operation of a carburetor throttle valve or other device requir inga more or less gradual and uniformimovement.

It is my object to produce a special solenoid and plunger structureand means whereby the magnetic pull on the plunger. will vary directly with current input and also. means and method of effecting a slightly delayingor retarded action of theplunger to any desired degree, on both the energized and the; de-energized movement of same.

It is also my object to provide methods and means whereby the energized movement of the plunger may be more rapid than the de-energized movement or vice versa.

' Another object is toprovide'method and means whereby the plunger will be immune -to-sudden shocks or vibration and incapable of sudden or violent movement.

I attain these and other objects of my invention by the mechanism illustrated in the accompanying drawings, in which- Figure. 1 is a side elevation of my solenoid and plunger, showing the adjustable bracket mountin ,Flg.:2 is a vertical section of my solenoid and plunger assembly on the center line 2-2 of Fig. 2, showing the plunger rod connected to a carburetor throttle arm; Fig. 3 is a section on line 33 of Fig. 1;

Fig.4 is a View partly in section and partly in elevation of a modified plunger construction;

Fig. 5 is a diagram of circuit connections to solenoids through the master control unit-=(rheostat); and

Fig. 6 is asection on line 6-6-of Fig. 2;

Like numerals indicate like'parts in each of the views.

With reference to the drawings and especially Figs. -1 and 2, a brass tube I is provided within which the iron plunger 2 is fitted. A brass plunger rod 3; threaded on one end, is screwed securely into the upper end of the iron plungerand soldered thereto, as indicatedat 4.

The upper end of the rod3'is provided with a U-shaped fulcrum member 5 which is securely affixed to said rod. The member 5 is connected to theslotted throttle arm 6 by means 'of the fulcrumpin 1, which provides for the free movement of said arm 6 without side pressure on the rod 3 and permits rigid vertical mounting of the solenoid unit.

A tapered hardwood or Bakelite sleeve 8 is bored for an easy fit on the tube I, as shown. A circular iron pole piece 9 is provided with a brass bushing 35 which is pressed securely in the member 9 and this assembly of pole piece and bushing is affixed to thetube l. a short distance from its upper extremity by soldering or otherwise. The tapered sleeve 8 extendsdownward to a point approximately level with the top of the iron plunger 2 when the-latter is in the full downward position shown.

The bottom iron pole piece I!) is 'emplaced on the'tube l a predetermined distance below the pole piece 9 and soldered thereto. This member ID is provided with a hub which is machined to fit in the mounting bracket H and is threaded the rest of its length, as shown at l2. A guard tube I3 is screwed tightly on the threaded end of said hub to clamp the solenoid assembly securely to the mounting bracket H, as shown.

The members 9 and Illform 'a spool on which the winding [4 is emplaced. A seamless steel tube I5 is provided with an easy push fit over the pole piece members 9 and i0 and is emplaced thereon after the coil winding is completed. This member I5 completes the magnetic circuit from members 9 to ID and also acts as a shield for the winding M which occupies the entire space 16. The starting end'of said winding may be grounded on the tube l, as shown at IL'orit may be brought out as an insulated terminal of the winding, if desired. The'finish'end 'ofthe winding must bei'risulated in theconventional manner, as shown at l8 and preferably connected to an insulated terminal post (not shown) which may be positioned on a suitable terminal block l9. After the member is emplaced as shown, it may be secured in position by one or more brass pins 20, driven tightly into holes provided in the member 9, as shown.

The plunger 2 is machined to a diameter that will provide a predetermined clearance within the tube I. Beginning close to the upper end it is turned taper for a predetermined length and to a predetermined degree, as shown. This taper stops at a predetermined distance from the extreme bottom end of said plunger, leaving a shoulder at which point one or more transverse holes ar drilled through the small end of the taper and holes are also drilled in the extreme bottom end of the plunger, upwardly to communicate with the transverse holes, whereby to form oil ports substantially, as shown at 22. A central hole is also drilled in the center bottom end of the plunger to provide a drive fit for the brass pin 23. A Bakelite washer 24 is pressed against the bottom end of the plunger by the spring 25 to normally close the oil port holes and this spring and washer are held in place by the brass pin 23, thus comprising a fluid release valve for the upward or energized movement of the plunger, the lower end of the tube I having a fluid tight plug 26, as shown. A drain hole 21 is provided in the lower end of the guard tube l3. At the extreme top end of the tube I, a cupped or cup-shaped dust cover 28 of soft leather is provided, which has a clearance hole for the rod 3 and which is securely clamped in place, as shown at 29.

The mounting bracket II is bolted to a rigid support whereby the solenoid assembly may be mounted with the plunger rod in line with the throttle valve arm 6. The slot I la in the bracket permits of vertical adjustment of the entire solenoid assembly.

The tapered sleeve 8 provides for a conical core of the winding over a major length of same and, also, at its upper end, provides for a maximum air-gap between the pole piece 9 and the plunger when the latter is in the extreme upper or energized position. The tapered portion of the plunger provides for a uniformly reduced mass or plunger cross-section entering the coil field when the latter is energized; the combined effect of which is (when these factors are properly proportioned) to produce a magnetic pull on the plunger directly proportional to the current input and not inversely as the square thereof, as is the case with a simple coil and straight plunger.

Very little energy is required to move the throttle arm and valve, but sufllcient energy input is required to lift the plunger. This energy input would not hold the plunger and throttle valve rigid at any given position, against bumps or vibrations however and therefore other means must be provided for this purpose.

It will be noted that when the coil is energized, the plunger moves upwardly to close the throttle and when the coil is deenergized, the plunger moves downwardly by gravitational action to open the throttle and that this gravitational action may be supplemented by a suitable spring, if desired.

Now, in order to prevent too rapid a movement of the plunger in either direction and also to prevent unwanted plunger movement due to bumps, shock or vibration, I provide for the use or a suitable fluid within the plunger tube I. This fluid may be a light oil of low viscosity, the normal level of which within the said tube is approximately shown at 30 (Figure 2), when the plunger is in the de-energized position shown.

In the present structure and its application, as shown in Figures 1 and 2, it is desirable that the plunger should move upwardly to close the throttle, with less resistance to its movement than when it moves downwardly to open the throttle. In other words, the hydraulic reaction on the plunger is relieved to a large extent on its upward movement by the opening of the release valve 24, thus permitting fluid to pass through the ports 22 to the lower end of the tube I, the rapidity of this movement being directly proportional to current input into the coil and the clearance space at the top end of the plunger. The latter cannot move upwardly any faster than the fluid is displaced to the lower end of the tube I because of the suction created below the valve 24 the instant the plunger starts upward. When the coil input is reduced or out off entirely and the plunger starts downward, the valve 24 remains closed and fluid displacement from below to above the plunger must take place through the small clearance space between the upper and lower ends of said plunger and the tube wall, the degree or amount of which clearance space will determine the rate of movement of said plunger and the throttle toward the latter partial or full open position. Thus, the throttle is caused ,to close more quickly than it can open.

As the plunger moves downwardly, displacing fluid in the lower end of tube I, this fluid moves upward past the sides of the plunger to above same and adds its weight to that of the plunger, which causes a gradually accelerated movement of the plunger downward, thus causing the throttle valve to start to open slowly and then with a gradually accelerated motion until stopped and held at any desired opening by the required current input into the coil, which is varied by the manually controlled rheostat 32--3'l (Figure 5), as shown. If the input to the solenoid is suddenly cut off for any reason, the throttle valve, actuated by the plunger, would move to the full open position more or less slowly-never suddenly or violently, an operating condition which is absolutely essential on multi-motored aircraft, as otherwise great damage might result. Hence, regardless of how rapidly the master control (rheostat) is operated, or the sudden disruption oi. a circuit or circuits, the rapidity ofplunger and throttle valve movement would be under absolute pre-determined control.

Means are disclosed in my pending United States patent application Ser. 415,495, whereby auxiliary controls connected in the circuit arrangement permit the pilot to accelerate any one or more motors and idle the others and it will be understood that this improved solenoid and plunger structure is specifically designed to be employed with the circuit and control methods therein specified.

In Fig. 6, I show how two or more of the solenoids are connected to a current source 34, one side of which is grounded, thence through a switch 33, through a variable rheostat 32, to each of the insulated terminals of the solenoids, through their coil windings and to ground. This circuit diagram is shown here merely to.illustrate how current is or may be varied to the solenoids or cut off entirely.

In certain other applications of my solenoid, it may be desirable to provide for a rapid plunger movement in the downward direction and a slower movement in the upward direction. To meet this requirement, I show a modification of plunger construction in Fig. 4, wherein the release valve and oil ports are positioned at the upper end of said plunger. Otherwise, the construction is substantially the same and either type plunger is interchangeable with the solenoid structure herewith described.

In high altitude flying where the temperature is very low, or in low altitudes in very low temperatures, multimotored planes experience great difiiculty with their throttle controls; the mechanical type contracting and binding, while the fluid in the pipe lines of the hydraulic type thickens, due to the cold. With my improved solenoid structure, which would be installed close to the engine, the fluid therein would not be affected by cold and regardless of the distance from the control panel to the motors, there would be little change in the resistance of connecting wires due to cold and whatever slight variation there might be, would be uniform in each circuit. For these and other reasons, my solenoidthrottle control is far superior and more dependable than any device now in use, particularly when employed in conjunction with the controls and circuits of the above mentioned pending patent application, which provides for maximum flexibility of the remote control of aircraft engines.

What I claim is:

1. In an electro-hydraulic solenoid, the combination of a plunger rod, a plunger secured to the rod, a. plunger tube closed at both ends and in which the plunger is slidably mounted, said plunger having a conically tapered portion whereby with the tube to provide an annular clearance chamber, oil ports extending from said chamber to the lower end of the plunger, a release valve normally closing the oil ports, spring means for normally retaining said release valve in closed position, a tapered sleeve externally mounted on the plunger tube, said sleeve being spaced at its upper end from the upper pole piece, a spiral winding, a tube enclosing said Winding, top and bottom pole pieces to which said tube is aflixed, the bottom pole piece having a threaded hub, and a guard tube secured to said threaded hub and enclosing and spaced from the lower end of the plunger tube.

2. In an electro-hydraulic solenoid, the combination of a plunger rod, a plunger secured to the rod, 21. plunger tube closed at both ends and in which the plunger is slidably mounted, said plunger having a conically tapered portion whereby with the tube to provide an annular clearance chamber, oil ports extending from said chamber to one end of the plunger, a release valve normally closing the oil ports, spring means for normally retaining said release valve in closed position, a tapered sleeve externally mounted on the plunger tube, said sleeve being spaced at its upper end from the upper pole piece, a spiral winding, a tube enclosing said winding, top and bottom pole pieces to which said tube is affixed, the bottom pole piece having a threaded hub, a guard tube secured to said threaded hub and enclosing and spaced from the lower end of the plunger tube.

HARLIE O. PUTT. 

